In modern high performance liquid chromotography (HPLC), pressures of several thousand lb/in.sup.2 are often developed within the chromatography columns. This requires that the column packing materials be rigid and non-collapsible. To achieve this, porous inorganic materials, such as silica and alumina, have heretofore been utilized as the support material with organic stationary phases on the surface to obtain a variety of liquid chromatography column packing materials.
Previously prepared porous chromatographic packings with a stationary organic phase have used covalent bonding to attach the organic phase to the support surface. The coupling of an organic phase (P) to the surface of an inorganic support has been achieved through the use of an intermediate silane coupling agent wherein the silicone portion of the molecule is bonded to the support and the organic portion of the organosilane either is the organic phase or is attached to the organic phase. Such inorganic supports are shown, by way of example, in U.S. Pat. Nos. 3,983,299 and 4,029,583.
The primary function of the coupling agent is to provide a chemical bond between the inorganic support and the stationary organic phase (P) that is responsible for the chromatographic partitioning. The general chemical formula for this composite may be expressed as: ##STR1## where .tbd.Si indicates that three of the bonds on silica are bonded directly to the inorganic support or to adjacent organosilanes that are bonded to the support, --CH.sub.2).sub.m is a coupling arm that ties the rest of the stationary phase (P) to the support, and m is a number ranging from 0 to 18.
In the preparation of chromatography packings it is necessary to strive for exact reproduction of the organic coating from batch to batch. It has been observed, however, that when an inorganic support is treated with a solution of organosilane it is difficult to reproducibly control the amount of organosilane that is deposited on the surface, particularly since many ways have been developed whereby organosilanes may be bonded to an inorganic surface. Chromatographically, the amount of organosilane deposited on the surface of an inorganic support is quite important. The chromatographic behavior of a bonded phase packing material is totally dependent on the nature and amount of organic material on the particle.
A further disadvantage of the organosilane bonding chemistry is that the bonded phase has been found to erode. As columns are operated and hundreds of column volumes of mobile phase pass through the column, organosilane hydrolysis can occur as follows: ##STR2## Although this reaction can be quite slow, it can still produce a substantial degradation in a relatively short period of time, as for example, in one month of continuous operation.